The Last Line of Storms from the 14 April 2012 Tornado Outbreak

The second major tornado outbreak of the year took place on 14 April 2012 (after the 2 March outbreak that slammed Indiana and Kentucky). At last count, 115 tornadoes were reported from Oklahoma to Iowa. Credit must be given to the Storm Prediction Center, National Weather Service offices, and local TV and other media outlets for accurately predicting the severe weather event and keeping people informed as it happened, and the people of the area for paying attention to the weather. It must be counted as a success on many levels that 115 tornadoes over 4 states only resulted in 6 deaths (and those deaths occurred in the toughest situation to warn people – a rain-wrapped tornado in the middle of the night where the tornado sirens were disabled due to a lightning strike earlier in the day).

The last bout of severe weather occurred with a squall line that formed in the late evening (~02:30 UTC 15 April 2012) along the dry line in western Texas and quickly expanded into Oklahoma and Kansas. This line produced the deadly tornado in Woodward, OK, along with many reports of 1-2″ diameter hail. Suomi-NPP passed over this line of storms between 07:45 and 07:50 UTC (15 April). The high resolution infrared window band, I-5 (11.45 ยตm), shows the immense scale of this storm system stretching from Wisconsin and Minnesota to Texas, in great detail. Be sure to click on the image, then on the “1497×1953” link below the banner to see it in full resolution. (The full resolution image is ~2MB in size.)

View of a squall line over the Central Plains from VIIRS channel I-5, 7:45 UTC 15 April 2012

View of the squall line over the Central Plains from VIIRS channel I-5, 7:45 UTC 15 April 2012

The color scale here is the same one used for the 2 March 2012 tornado outbreak image and the 25 January squall line over southeast Texas. The darkest blue pixels visible amongst the white overshooting tops (more easily visible on the southern end of the squall line) have a brightness temperature below -77 C, indicative of very strong convection.

A squall line over Texas as seen by VIIRS

VIIRS RGB "true color" composite

A severe squall line formed over eastern Texas on 25 January 2012. There were 19 tornado reports and 48 reports of wind damage, including “a house destroyed by a possible downburst”, according to the Storm Prediction Center. The high resolution imager on VIIRS captured this squall line as it was rapidly intensifying. Shown below are images collected from channel I-5, the high-resolution infrared window channel (11.45 μm). (Click on images for full resolution.)

VIIRS Channel I05

A squall line over eastern Texas observed by VIIRS channel I05 (11.45 um) at 19:24 UTC on 25 January 2012.

This squall line had several overshooting tops over the Gulf of Mexico that reached a temperature of -77 C. A zoomed-in view of these tops are shown below.

VIIRS Channel I05

A squall line over eastern Texas observed by VIIRS channel I05 (11.45 um) at 19:24 UTC on 25 January 2012.

The dark blue pixels near the center of the image indicate an overshooting top approximately 5 km in diameter where temperatures were less than -77 C. Several pixels in a storm top at the bottom center of the image and in a storm top at the top center of the image (near Galveston, TX) also reached that temperature.

A sounding was taken at 18:00 UTC at the Lake Charles, LA, National Weather Service (NWS) office, which observed a minimum temperature of -74 C at 17.9 km above sea level, indicating that these are some tall thunderstorms. Image courtesy the University of Wyoming.

Radiosonde sounding

NWS sounding taken at 18:00 UTC from the Lake Charles, LA office.

The VIIRS imagery was collected right as the squall line was intensifying. Shown below is the radar loop from the Houston/Galveston radar between 18:00 UTC and 21:00 UTC. Note, at the beginning of the loop, the southern end of system consists of two rather disorganized lines of cells. These lines of cells merge at around 19:25 UTC (the time of the Suomi NPP overpass), and a much stronger and more organized squall line develops.

Radar loop

Radar loop from the Houston/Galveston NWS WSR-88D radar beginning at 18:00 UTC, 25 January 2012.

At roughly 375-m resolution at nadir, the I-5 channel on VIIRS is providing some of the highest resolution infrared imagery available to the atmospheric science community. We are just beginning to see the capabilities of this powerful instrument.